The Formation of Hydrogen-Bond Facilitated Salts with Tunable Optical Properties: An Experimental and Theoretical Study of 2,4,5-Triphenylimidazole

Adjusting and modifying the optical properties of organic fluorophores are of importance for the development of the next generation of luminescent materials. Herein, we report the tunable fluorescence of 2,4,5-triphenylimidazole (TPI) chromophore by the formation of multicomponent crystals with the supramolecular building blocks, 4-bromotetrafluorobenzene carboxylic acid and tetrafluorosuccinic acid, by means of hydrogen bonding. A change in packing fashions between two adjacent TPI molecules is observed from a staggered pattern in the pure TPI crystal to an antisymmetric parallel arrangement in the multicomponent crystals. Moreover, the obtained organic salts show red-shift emission and enhanced fluorescence lifetime compared with the pure TPI crystal. Periodic density functional theoretical (DFT) calculations suggest that the introduction of the coformers can influence the energy level structures and orbital distributions of the TPI chromophore in the multicomponent crystals. Therefore, by the combination of experimental and theoretical studies on the multicomponent organic solids, this work not only reports the supramolecular assembly of new types of photoactive solid-state materials but also provides a detailed understanding of the electronic structures of the luminescent materials.